Field of the Invention
The present invention relates to a method for estimating channel parameters of radio channels of a W-CDMA mobile radio system in which sequences of known symbols are transmitted between unknown data symbols by a base station. The channel estimation is carried out by comparison of the received sequences with the known symbols, and the result of the comparison is integrated over a sequence of known symbols.
The present invention is concerned with the problem of channel estimation in cellular radio systems with W-CDMA (wide band code division multiple access), such as the one described in detail, for example, in the literature in P. Jung “Analyse und Entwurf digitaler Mobilfunksysteme” [Analysis and Design of Digital Mobile Phone Systems], B. G. Taubner Verlag, Stuttgart, Germany, 1997, and in the periodical IEEE Transaction on Vehicular Technology, volume 47, No. 4 of November 1998 in the article “W-CDMA The Radio Interface for Future Mobile Multi-Media Communication”. That method is of considerable importance because it is intended to form the worldwide standard for third-generation mobile phone technology, as explained in IEEE Transactions on Vehicular Technology, volume 47, No. 4 of November 1998 in the article “UMTS Universal Mobile Telecommunication Systems: Development of Standards for the Third Generation”.
In mobile phone systems, it is always necessary to take into account the problem of the movement of the mobile receiver continuously changing the properties of the transmission channels. It is of overriding importance that the respective receiver has the best possible hypotheses with respect to the channel parameters at a given time, in order to ensure a good degree of detection of the transmitted signals.
For that purpose, various physical channels for channel estimation are to be provided at the system end in the future UMTS standard for mobile phone systems. On the one hand, a sequence of symbols, which are known by the subscriber, referred to as dedicated pilot symbols, is transmitted to a specific subscriber by a base station. On the other hand, in continuous operation for all subscribers, the base station transmits a sequence of pilot symbols, which is known to the subscribers on a common channel, referred to as the common pilot channel.
The most pertinent prior art relates to the currently available mobile phone system ANSI-95 (in the USA). However, the system makes exclusive use of the estimation of the channel parameters using the common channel, and the signals that are emitted on that channel and are known to all subscribers (i.e., common pilot signals). The ANSI-95 system uses algorithms from the prior art that are based on channel estimation using integration over the pilot signals for this purpose.
However, it has the disadvantage that the transmission power, which is used for the common channel and the spread factor are not necessarily also suitable for the channel that the specific subscriber is using. The greater the difference in power or the difference in spread factors with which the various channels are transmitted, the greater the systematic error in the determination of the channel parameters for the channel of the individual subscriber as a result of simply transferring the channel parameters of the common channel.